This invention relates generally to a printer head and more particularly to a dot printer head used to print on paper by means of a plurality of needles or wires impacting on paper through an ink ribbon. Various structures for mechanical dot printer heads have been developed. This invention relates to a dot printer head which comprises print wires and magnetic devices to drive and selectively extend the print wires upon the occurrence of a printing signal, so that printing may be performed as required on recording paper. More particularly the print head of this invention is of the type wherein magnetic forces produced by magnetic devices are transmitted individually to each print wire through an operating lever thereby indirectly driving the print wires.
The printing action is produced by pivoting the lever about one lever end which acts as a fulcrum. The other end of the lever drives the print wire through a wire guide which aligns all of the plurality of print wires. Therefore, the contacting portions of the operating levers against the print wires, and the fulcrum points are most likely to be worn due to the relative motion between cooperating members under high contact pressure. The durability of these contact points is a major factor in determination of the operating life of the print head.
In order to improve the wearing qualities of these parts in the prior art, the following measures have been adopted. First, the surface hardness at the points of contact of the members has been increased. However, this method has its limitations and is not effective in situations where wear is caused by chemical action, especially in the cases of abrasive corrosion. Moreover, such a hardening technique increases the cost of production. Secondly, lubricants such as grease have been applied. However, in a wire type dot printer head wherein each part repeatedly performs a recipricating motion at high speed, the use of a grease type lubricant has several deficiencies. Namely, because the lubricant disperses very quickly, it is difficult to maintain good lubricating properties over an extended period of time. The splattered lubricant of itself, or a mixture of foreign substances cohering with the lubricant, adheres to the inside of the printer head causing poor operation thereof. Also, at low temperatures, the high viscosity of the lubricant under those conditions often causes a sticking phenomenon.
Accordingly, what is needed is a wire type dot printer head which has a long life as a result of effective lubrication at wear points. Further, it is desirable that the lubricant not cause sticking at low temperatures and the lubricant should not splatter during operation of the printer head.